O.S. Engines 2CK Carb - 22781010 - Manual

O.S. 2B-2CB-D-2CK
INSTRUCTIONS FOR O.S. TYPE 2B, 2CB-D & 2CK AUTOMATIC CARBURETTOR
This new carburettor incorporates an automatic mixture control device which ensures that the engine receives a
correctly balanced mixture of fuel and air at all throttle settings. The device progressively reduces the effective size
of the fuel jet orifice as the throttle is closed, thereby preventing the engine from running too rich at low speeds. This
also means that an airbleed is no longer required and, with its elimination, maximum suction is maintained at the fuel
jet at all times. This is a most important factor where manoeuvres have to be executed at low engine speeds and
through wide variations of fuel level within the fuel tank.
Under average operating conditions; the carburettor will
normally function satisfactorily as factory set. Simply start the
engine in the normal way and adjust the needle-valve for maxi-
mum r.p.m. On closing the throttle, the engine should idle at
between 2,500 and 3,000 r.p.m. and also run steadily at all
intermediate speeds. However, different fuels and/or climatic
conditions, may require minor readjustments for optimum
results.
Throttle Rotor Set-Screw
Lock Nut
Needle Valve
Mixture Control Screw
Photo shows carburettor
type 2B
2B
NOTE: In the event of the factory carburettor settings having
been accidentally disturbed — or otherwise interfered with
provisional settings may be re-established as follows:
(1) Release Throttle Rotor Set-Screw Locknut and unscrew
Throttle Rotor Set-Screw just sufficiently to allow the
throttle to close completely.
(2) With the Throttle Rotor set as above, carefully screw in the
Mixture Control Screw until it stops. Do not force Mixture
Control Screw beyond this point as its tapered tip may
damage the fuel jet hole. Now unscrew the Mixture Control
Screw 1 1/2 turn from this point.
(3) If, necessary, fine-tune the carburettor in accordance with
the procedure explained below.
ADJUSTING THE CARBURETTOR
Three adjustable controls are provided on this carburettor:
( 1 ) The Needle Valve (located on left-hand side of
carburettor).
(2) The Mixture Control Screw (located on right-hand side).
(3) The Throttle Rotor Set-Screw (angled at rear of body).
I. The Needle-Valve is used in the same way as on all model
engines, i.e., for adjusting the hiqh-speed mixture strength.
Start the engine and, with the throttle fully open, gradually
close the Needle-Valve until it is running at its maximum
speed. Caution: Do not close Needle Valve to too "lean" a
setting as this will cause the engine to overheat and slow up.
Set the Needle-Valve very slightly to the "rich" side of the
peak r.p.m. setting. Make sure that the engine is fully
"broken-in" (about 1 hour of total running time in short runs)
before operating it continuously at full throttle.
II. The Mixture Control Screw is for adjusting fuel mixture
strength at part-throttle and idling speeds. Having set the
Needle-Valve as detailed above, close the throttle. The engine
should idle continuously and steadily without further
adjustment.
(a) If, however, the engine begins to idle unevenly, open the
throttle. If the engine then hesitates before picking up to full
speed, it is probable that the idling mixture is too rich. Check
this by closing the throttle again and letting the engine idle for a
little longer before again opening up. If the engine now puffs out
a good deal of smoke and hesitates or even stops, it will be neces-
sary to close the Mixture Control Screw. Do this by turning it
clockwise about 10 ~ 20 degrees turn should be sufficient.